Polymer resin-laminated structures are designed pursuant to their application purposes. Generally, resin moldings having different properties and/or made by different molding methods are bound to form a resin-laminated structure having new features. For preparing an interior automotive trim (e. g., instrument panel), an exterior layer of soft resin prepared by sheet molding and a base layer of quite hard resin prepared by injection molding are bound to form a resin-laminated structure having excellent strength, impulse-durability and acoustic absorptivity together with soft surface quality in feeling.
The resin-laminated structures consisting of the exterior layer and the base layer are fabricated by independently molding the exterior layer and the base layer and binding them to each other. This binding between the exterior layer and the base layer is performed with thermal vacuum molding or thermal adhesion molding. These binding methods are described below.
Vacuum molding methods are disclosed in Korean Patent Laid-Open No. 199958663 and Japanese Patent Laid-Open No. Hei11-343477. According to these patent applications, an exterior layer of soft polyvinylchloride sheet is fixed to a mold with vacuum adsorption, and a base layer of polycarbonate composite resin is also fixed to the mold. After the objects to be adhered are sufficiently pre-heated, polyurethane foaming material including adhesive material is injected between the exterior layer and, the base layer to perform foaming and compression molding. This vacuum molding method has an advantage that the adhesive strength between the exterior layer and the base layer is good, because the objects, namely polyvinylchloride, polycarbonate and polyurethane, are all polar resins.
However, this method has shortcomings: expensive vacuum apparatus and compressive equipment operated at high pressure are required, the objects may be deformed during the pre-heating, recycling of the used materials is impossible because it is not-easy to extricate the resin-laminated structure into pieces, the non-uniformity of foaming material may produce inferior products, shrinkage and irregularities may happen to the exterior layer when both vacuum and heat are supplied, and finally the plasticizer included in soft polyvinylchloride is harmful to humans.
A thermal adhesion molding method, which is more advanced in view of recycling used materials than the vacuum molding method as described above, is disclosed in Japanese Patent Laid-Open No. Hei12-282001 and Korean Patent Laid-Open No. 199943059. According to these patent applications, the thermal adhesion molding method is a method that after an exterior layer of polyolefin resin and a base layer of polyolefin composite resin are sufficiently preheated, the objects are compressed at high pressure using an adhesive agent therebetween or heat to form a resin-laminated structure. This thermal adhesion molding method has an advantage that the resin-laminated structure can be recycled.
However, this method has shortcomings. The base layer consists of polyolefin resin as a non-polar resin which lacks strength and whose adhesive force to the exterior layer is not good; thus the exterior layer may be stripped from the base layer, the working environment is not pleasant due to a malodor of adhesive agent and the like, the objects may be deformed during the pre-heating, and equipment operated at high temperature and pressure is additionally required.
In order to improve the shortcoming of the deterioration of adhesive force between the base layer and the exterior layer as described above, a method proposed is that a primer layer should be previously coated on the base layer, or that the base layer or the exterior layer be surface-treated with plasma, corona, electron ray, high frequency wave, heating by hot air, or flame treatment.
The above-mentioned method can improve the adhesive force between the base layer and the exterior layer. However, the method has shortcomings. In the former case of previously coating the primer layer on the base layer some processes should be added and thus the productivity decreases, whereas in the latter case of surface-treating the base layer and the exterior layer, additional expensive equipment is essential and thus the fabrication cost increases.